Evidence for collectivity in pp collisions at the LHC

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• 作者：The CMS Collaboration^⋆ ; V. Khachatryan ; A.M. Sirunyan ; A. Tumasyan
• 关键词：CMS ; Physics ; Heavy ion ; Ridge ; Correlation ; pp
• 刊名：Physics Letters B
• 出版年：2017
• 出版时间：10 February 2017
• 年：2017
• 卷：765
• 期：Complete
• 页码：193-220
• 全文大小：1807 K
• 卷排序：765

文摘

Measurements of two- and multi-particle angular correlations in pp collisions at s=5,7, and 13TeV are presented as a function of charged-particle multiplicity. The data, corresponding to integrated luminosities of 1.0pb−1 (5 TeV), 6.2pb−1 (7 TeV), and 0.7pb−1 (13 TeV), were collected using the CMS detector at the LHC. The second-order (v2v2) and third-order (v3v3) azimuthal anisotropy harmonics of unidentified charged particles, as well as v2v2 of KS0 and Λ/Λ‾ particles, are extracted from long-range two-particle correlations as functions of particle multiplicity and transverse momentum. For high-multiplicity pp events, a mass ordering is observed for the v2v2 values of charged hadrons (mostly pions), KS0, and Λ/Λ‾, with lighter particle species exhibiting a stronger azimuthal anisotropy signal below pT≈2GeV/c. For 13 TeV data, the v2v2 signals are also extracted from four- and six-particle correlations for the first time in pp collisions, with comparable magnitude to those from two-particle correlations. These observations are similar to those seen in pPb and PbPb collisions, and support the interpretation of a collective origin for the observed long-range correlations in high-multiplicity pp collisions.